Process for making electrolytic iron



R. D. PIKE PROCESS FOR MAKING ELECTROLYTIC IRON July 1, 1930.

Filed March l5, 1926 DNZOQQ M l) IMZMtIL.

INVENTOR. @0240/ nlvcDl KNEE Patented July i, 1930A UNITED STATES"PATENT OFFICE.

ROBERT D. PIKE, F PIEDMONT, CALIFORNIA. PRCESS FOR MAKING ELECTROLYTICIRON Application led March 13, 1926. Serial No. 94,454.

My present invention relates to a process for making electrolytic ironfrom leach liquors in non-diaphragm cells, and includes l a leachingprocess whereby iron and/or cop- 6 per is dissolved by the action offerrie iron on metallic iron and/or copper ores and the iron dissolvedfrom the metallic ironand/or copper ores and that used for removingcopper and-fother metals (if present) `from solu- 10 tion, is depositedelectrolytically in a cell without diaphragms, but having insolubleanodes; such deposition of iron resulting in the regeneration of theliquor for further leaching operations.

Under conditions known hitherto, if iron were to be plated out ofsolutions in electrolytic cells with insoluble anodes, it has beennecessary to employ diaphragms to separate the anolyte from thecatholyte, if commercial current eiciencies were to be obtained.

This is because of the wellknown fact, based upon the principles ofelectro-chemistry, that ferric iron in contact with a cathode will bereduced to ferrous iron before metallic iron can be plated out. This isexplained electrochemically by the following equations:

These equations show that deposition of iron cannot occur theoreticallywhen Fem is in contact with the cathode.

I have found in practice that if the electrolytic iron cell withinsoluble anodes be run at 70 centigrade or above, with ferrous chlorideleach solutions containing about 12% Fe, even small percentages offerrie iron as low as .1% in the cathoyte will seriously lower currenteicienc hese are the conditions ysubstantially o taining in my formerapplications, Serial Numbers 58,012, 58,009?, and 58,010 (all filedSeptember 23, 1925 and Serial Number 87,509, filed February 11, 1926, inall of which inventions I employ diaphragm cells and keep theconcentration of Fe'f substantially,7 below .05%.

I have discovered that if I employ as the electrolyte a solution offerrous chloride containing preferably about 12% iron in a nondiaphragmcell with an insoluble anode of ksulphide Yrelatively cold dilutesolutions of ferric the type hereafter described, at abputroomtemperature, and use a current density of preferably 7 amperes persquare foot, and

operate the cell so that the eiiluent containsl a It is possible to cmloy widevariationin the concentration an composition of theelectrolyte,.in the current density and temperature employed, withoutdeparting from -the scope of my invention. For example, in practice theelectrolyte will tend to'assume a temperature of from 20 to 30centigrade, or a littleabove actual room temperature, and this issatisfactory, although I have found it to be a general rule that theeffect of Fe**+ in lowering current eiiciency becomes the morepronounced the higher the temperature; and on this account, if it isdesirable, as is sometimes the case, to heat the leach solutions forpromoting extraction of metals, the reduced liquors should be cooled by'spraying or other suitable device before returning to the electrolyticiron cells.

f sponge iron or iron scrap is the raw material employed it isunnecessary to heat the leach solutions to promote efficient extraction;but ifv the raw material isfa sulphide mineral, such, for example,as'l'chalcocyte, bornite, or even chalcopyrite, thev leach solutionsshould be heated, and in the case of `the last-mentioned mineral, toboiling. Some other sul bide minerals, notably galena (lead l), are moreeasily decomposed by chloride. A preferable method for proceeding is tomake sponge iron from copper and precious metal be'arlng cinders frompyrite roasters. The leaching of such iron 1s so conducted, as describedhereafter, as to effect a complete separation of the iron from the morenoble metals, i. e., copper, silver,`and gold; and these last-named arerecoverable as valuable by-products. y

In the accompanying drawing,

The figure illustrates a flow sheet for production of electrolytic ironfrom sponge iron. With slight modifications, as described below, thisflow sheet may be applied to the treatment of any of the materials abovementioned. t

Itwill be understood that there may be considerable variation from thedescribed flow sheet; as, for example, in the composition of the leachsolutions and the manner of their application, without departing from myinvention, and also thaty diaphragm cells may be employed, if desired. y

Referring in detail to the drawing, return leach from the electrolytictank house, containing about 12% total iron as chloride, of

which about .75% is ferrie iron, and at a temperature of 20 to 30centi-grade, enters the agitator 1, where it meets the underflow fromthe thickener 2, as well as the clarified liquor from the filter 3. Thedischarge from agitator 1 goes tothickener 4, the underflow of whichgoes to filter 3. The cake from filter 3 is the exhausted tails freefrom iron, copper, and other metals which the original sponge iron mayhave contained.

The overflow from thickener 4 is pumped by pump 5 to agitator 6, whereit meets the underflow fromthickener 7. Agitator 6 discharges intothickener 2. The overflow from thickener 2 goes to agitator 8, where itmeets the fresh sponge iron, and the agitator 8 discharges intothickener 7. The overflow from thickener 7 is completely reducedcopper-free electrolyte. The system described of thickeners 2, 4, 7 andagitators 1, 6, 8, is in effect a counter-current leach arrangement inwhich the fresh sponge iron completes reduction of the leach, and thefresh leach completes solution of the iron.

However, the sponge iron may contain copper and/or other metals whichareelectro-negative to iron; and such metals may be completely dissolved inagitator l, and completely precipitated in agitator 8. They willtherefore accumulate in the leaching system. To counteract thistendency, a portion of the overflow from thickener 4 is bled to agitator9, where sufficient sponge iron is added to precipitate all of thecopper and' other metals electro-negative to iron. Agitator 9 dischargesinto thickener 10, the underflow of which passes to filter 11, the cakeof which is principally cement copper and may contain other metals. Theclear liquor from lter 114 returns to agitator 9. The

overflow from thickener 10 j oins that from thickener 7.

The full flow of electrolyte is next treated in a tank 12 with H2S toprecipitate traces of Zn,

and other relative electro-positive metals. The sulphide precipitate isremoved in thickp ener 13 and filter 14. A discard may then be .replacedwith fresh ferrous chloride.

The electrolyte next goes to supply tank 15, and thence throughelectrolytic tank cells 16. These are of the ty e hereinafter described.The anodes are pre erably of plate graphite, and the cathodes steelsheets'with oxidized surfaces to facilitate stripping of theelectrolytic iron. The current density is preferably 7 amperes persquare foot, and the cell voltage about 1.75. The regenerated leach goes`to tank 17 and pump 18 returns it to agitator 1.

In treating chalcocyte, or other sulphide mineral, the same How sheet isemployed as in Fig. 1 except that the mineral, instead of sponge iron,is introduced into the agitator 8. With sulphide mineral there will beno appreciable accumulation of copper in the counter-current system, andall of the copper will be in solution in the overflow of thickener 7.This entire overflow will therefore pass through the copper cementationsystem 9, 10, 11, and this system will receive no liquor from any otherpoint in the counter-current system. After precipitating the copperand/or other relatively noble metals, the

vliquor passes to the tank 12, and thence on spray pond, or othersuitable device (not shown), should be employed, so as to deliver theelectrolyte in a relatively cool condition to supply tank 15.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The process of making substantially copper-free electrolytic ironfrom copper-bearing metallic iron which consists in dissolving the laterin a counter-current leaching apparatus with a leach liquor containingferric iron; bleeding a portion of the liquor from a point in thecounter-current system, treat- 0ing this bled portion with suiiicientmetallic iron to completely lreduce the ferrie iron in solution andcompletely precipitate copper in solution, then passing the completelyreduced and copper-free liquor discharged from this step, together withthe reduced copper-free liquor from the counter-current leach, toelectrolytic cells for the deposition of iron and the regeneration ofthe leach.

2. The process of making substantially copper-free electrolytic ironfrom copper-bearing metallic iron which consists in dissolving thelatter in a counter-current'leaching appamus with c leach qumc conuomgerc xom9 bieding a. portion o the liquor from a, point in checounser-cux'rem sysem, treating 'this bled portion with suciem'. meaicoL. to completey reduce the fem'c iron in scutiom and completelyprecipitate copper in sointion, then passing the completely reuced amicopper-free liquor discharged from this stepi together with the reducedcopper-free Equo? om the counter-current leach, to the top onon-diaphragm cells for she deposion o iron and the regeneration of theeach am Withdrawing the regenerated souton from the bottom of the cellsRBERT D. PIKE

